The WT1 gene (Wilms' tumor 1 gene) was identified as a causative gene of a Wilms' tumor which is a kidney cancer in childhood, and the gene encodes a transcription factor having a zinc finger structure (Non-Patent Documents 1 and 2, herein incorporated by reference). Subsequent studies showed that the above gene serves as a cancer gene in hematopoietic organ tumors or solid cancers (Non-Patent Documents 3 to 6, herein incorporated by reference).
It was shown that cytotoxic T cells (CTLs) specific to the peptide are induced by stimulating peripheral blood mononuclear cells in vitro using a peptide having a portion of an amino acid sequence encoding the WT1 protein, and these CTLs injure cancer cells of hematopoietic organ tumors or solid cancers expressing the WT1 endogenously. The CTLs recognize the above peptide in the form of a complex bound to an MHC class I molecule, and thus the peptide differs depending on subtypes of the MHC class I (Patent Documents 1 to 4, and Non-Patent Document 7, herein incorporated by reference).
On the other hand, the presence of helper T cells specific to a cancer antigen is important in order to induce the CTLs effectively (Non-Patent Document 8, herein incorporated by reference). The helper T cells are induced and activated by recognizing a complex of an MHC class II molecule with an antigen peptide on antigen presenting cells. Activated helper T cells aid proliferation, differentiation and maturation of B cells by producing cytokines such as IL-2, IL-4, IL-5, IL-6, or interferons. Since such helper T cells have a function to activate an immune system by promoting proliferation and activation of B cells and T cells, it is suggested that the enhancement of a function of helper T cells through an MHC class II-binding antigen peptide in cancer immunotherapy to enhance effects of a cancer vaccine is useful (Non-Patent Document 9, herein incorporated by reference).
It has recently been shown that a promiscuous helper peptide which can bind to multiple MHC class II molecules and activate helper T cells is present among particular peptides having a portion of an amino acid sequence encoding a WT1 protein (hereinafter, also referred to as WT1 peptides in the present specification) (patent documents 5 and 6, herein incorporated by reference). However, it was very difficult to verify whether or not the WT1 peptides also have effects on other MHC class II molecules, because of many kinds of MHC class II molecules.